This invention relates to the dyeing of textile fabrics, and in particular to a continuous process for dyeing textile fabrics formed at least partially of polyester fibers.
It is known from the technical literature (for example, W. Bernard Praxis des Bleichens und Faerbens von Textilien [Bleaching and Dyeing Practice of Textiles], Springer Verlag, 1966) and from pertinent publications that textile fabrics of polyester fibers and/or their blends with cellulosic fibers can be continuously dyed by the so-called "Thermosol Process." In applying this method, the fabric is impregnated with a cold to warm, aqueous dispersion of suitable dyestuffs and auxiliary agents to a defined weight increase, dried, subsequently "thermally fixed" at temperatures of 180.degree. to 220.degree. C., and again liberated from excessive dyestuff by washing. During the thermal fixation, the dyestuffs diffuse into the polyester fiber in a finely dispersed or monomolecular form, and are dissolved in the fiber. The advantage of this method is the possibility of simultaneously fixing the polyester fibers and obtaining very fast colors within a short period of time ranging from 40 to 120 seconds at 180.degree. to 220.degree. C.
A prerequisite for the success of the process is that the dyestuffs are already uniformly distributed in the textile product after the impregnation and intermediate drying. If not, nonuniform coloration will result. Another prerequisite is that the product is dried before the thermal fixation, since otherwise the temperatures for the Thermosol Process will not be reached because of evaporation of the dyebaths.
However, the Thermosol method has been found disadvantageous in practice, in that not all textile fabrics of polyester fibers can be dyed by this process, and that it is absolutely necessary to dry the product following the padding. In particular, it is not possible to dye pile fabrics by this method, since the dyebath migrates to the pile tips and bases during the intermediate drying, and thus, the product is dyed unevenly. Furthermore, the process is uneconomical, since the fabric needs to be dried twice during the dyeing process. Even though attempts have been made to overcome these disadvantages by the use of so-called migration inhibitors and special padding assistants, they have been unsuccessful in the case of the pile fabrics, such as, plushes, velvets and velours. A further problem with the pile fabrics, due to their high bulk and insulating characteristics, is that it is not possible to achieve Thermosol temperatures throughout the fabric in a reasonably short duration without overheating and fusing the tips of the pile yarns or leaving inner portions of the fabric insufficiently heated.
It is, therefore, an object of the present invention to develop a method for continuously dyeing polyester fibers and filaments and/or their blends with cellulosic fibers, which overcomes the aforementioned disadvantages and by which also pile fabrics can be satisfactorily dyed.